MONTPELIER — Tests have found more mosquitoes infected with the virus that causes the potentially deadly disease Eastern equine encephalitis, and the Vermont Health Department is urging people to protect themselves from mosquitoes during outdoor activities, especially over the Labor Day weekend.

The virus was found in a number of samples taken in swampy areas of Whiting, nearby Leicester, Brandon and Sudbury, the health department said.

“The entire area around this swamp system appears to be a hot spot for EEE,” said Health Commissioner Dr. Harry Chen in a news release Friday.

So far this year no human cases of EEE have been reported in Vermont; last year two people who lived near the swamp died of the disease. EEE strikes the central nervous system and kills about 35 percent of the people who contract a form of the illness.

“It’s definitely caught a lot of peoples’ attention,” said Tim Schmalz, chief of the plant industry section at the Vermont Agency of Agriculture who has been studying EEE.

Scientists have also detected West Nile virus in the state, including a human case and one in a horse. The human patient recovered.

The health department is urging anyone who goes outside during the early evening and morning hours when mosquitoes are most active to wear long-sleeved shirts and pants and use insect repellant. Property owners should also fix holes in door and window screens and reduce mosquito habitat by dumping out standing water.

There is evidence the EEE virus has existed for years across the Eastern U.S. and into Canada, said Erica Berl, a department infectious disease epidemiologist.

The mosquito that spreads EEE is found in a type of swamp, such as is found in northern Rutland and southern Addison counties.

“We think most of the risk is associated with living within five to 10 miles of a hardwood, acidic swamp. It’s not uniformly distributed across the area, but it seems to show up like hotspots. It seems to be associated with a particular wetland,” Berl said.

Schmalz said the virus builds up in birds and mosquitoes over the summer.

“Why it showed up in sufficient quantity to get out and infect humans (last year) is still a bit of a mystery,” he said. “There are a lot of questions that haven’t been answered, a lot of basic research on this disease that we could really use more information on.”

He said that because two people and some horses died from EEE in Vermont last year, the office has stepped up its efforts to understand the virus.